Photo-electric cell



May 27, 1930. R. K. POTTER PHOTO. ELECTRIC CELL Filed Sept, 8, 1926 INVENTOR RZPvtter ATTORNEY Patented a... 27.1936

This invention relates to photo-electric cells, and more particularly to photo-electric cells having a photo-sensitive cathode, an anode, a source of voltage connected between the elec rode terminals, and a gas content allowin ionization by collision.

In t e usual form of hoto-electric cell of this type, the output of the cell is roportional to the uantit or intensit of t e incident light. t is tl ie object 0 this invention to provide a satisfactory photo-electric cell which is responsive not only to variation in the quantity of the light butalso to the displacement of an incident light beam of constant intensity. Such a cell is advantaincluding special optical meansas a part of the device.

In general the cell embodying my inven-' tion is so arranged that the accelerating field over the region between the sensitive area of the cathode and the anode is graduated, the magnitude of the effective accelerating field being different for different positions of the light-beam.

"trodes of a photo-electric cell is suflicient to remove all of the electrons as fast as they are released from the cathode'by an incident light beam, and if there is no gas present in A the-cell envelope, the output will depend solely upon the quantity of light. Therewill be no change in the output current with anincrease of the anode potential. If, however,

gas is present in the tube, the output is no longer a simple function of the quantity of incident; light but de' ends upon the kind of gas, its pressure an temperature, the electrode spacing, and the strength of the accelerating field.- The electrons released by the photo-electric action cause ionization of the gas if the mean free path of the gas molecules is shorter than the path between the electrodes and if the accelerating field is strong enough to give an electron a suflicient velocity before it strikes. In familiar types of cell I many collisions take place inthe distance between the cathode andthe anbde. Since each collision releases more electrons, the acgeous, especially in certain reproduction methods in which it obviates the necessity of If the accelerating field between the elec-- NITED STATES PATENT'OFFICE? m1: x. 1 orrna, or raw roux, n. 2., assrenoa TO mnzucm 'rrmnrnonn Am) 'rnmenarn conrm, A OORPOBATION or NEW YORK,

rno'ro-nnnc'rmc CELL Application filed. September 8, 1926. Serial No.-134,301.

tion is cumulative. The total output current of a photo-electric cell of such type" may be represented by the following relation in which t is the current due to photo-electric efi'ect alone.

c is natural logarithmic base (constant),

p is the pressure of the gas in the cell,

d is the distance between the electrodes,

4 N and V are the ionization constants, and.

. stood from the following detailed description whenread with reference to the accompany-' ing drawing. Figure 1 of the drawing shows the cell in longitudinal section, and Fig. 2 is a cross-sectional view of the cell taken on the line 2-2 of Fig. 1. Likenumerals of reference in the two figures of the drawing deslgnate corresponding parts of thedevi'ce.

The electrodes of the cell are contained in an evacuated envelope 3. The cathode 4 is of a light sensitive material and is of a high reslstance, as is indicated diagrammatically in Fig. 1 of the drawiil the form of a wire con. uctor having a negligible resistance. The light beam enters the cell through the slit or window 6, shown in in Fig. 2 of the drawing. A battery 7 is connected across the terminals of the cathode 4, and a'second battery 8 in series with a meter 9 is connected between one terminal of the cathode and the anode as shown.

When the light beam falls'upon the cathode at any"; point, the resultant 'otential between the cathode and the anod; is the algebraic sum of the voltage of battery tential drop, from the left end of the cathode filed as of even date herewith The anode 5 takes 8, the po-- to the sensitized portion of the cathode (the battery 7 furnishing the voltage), and the potential drop due to the space current flow- 111g along the cathode to the point of electron release. If the light beam is'in the position alge from the left-hand terminal B falling V the resultant potential is the algebralc sum of the voltage of'battery 8, the potential drop of the cathode to the point :11, and the potential drop due to the space current flowing along the oathode to the point as. If the light beam takes the osition B the resultant potential is the upon the cathode at the point an,

the potential drop from the left-hand terminal of the cathode to the point 3 and the potential drop due to the space current flowing along the cathode to the point y.

7 It is to be noted that the action of the cell depends upon a variation of E of the relation stated above.

It will help to clarify the operation of my cell if the arrangement is viewed as being essentially a potentiometer circuit, the movable arm being ad'usted by the deflection of the incident light earn and having in series with it a resistance equal to the internal resistance of the cell under the conditions of operation.

It is to be understood thatthe form of the evacuated cellmaybe changed and otherstructural changes from the specific showing of the drawing may be made within the scope of the appended claims without a departure from the s irit of the invention.

at is claimed is: 1

1. A photo-electric cell responsive to, the displacement of an incident light beam, comprising a light-sensitive, double-terminal cathpde of high hmic resistance and an ano e.

2. In a. photo-electric cell, an envelope, a light-sensitive double-terminal cathode therein having high ohmic resistance, said envelope being adapted to admit a beam of light to fall upon said cathode at difierent points over a substantial range of'displacement of the beam, an anode, a source ofportential connected between one end of said cathode and said anode, and a source of potential connected between the terminals of said cathode, wherebythe efiective potential between the cathode and the anode for a given position of a light beam is the algebraic sum of the voltage of the source connected between the cathode and the anode, the potential drop between the end of the cathode connected to the anode and the point on the cathode sensitized by the incident beam, and

the potential drop due to the s ace current flowing along the cathode to said sensitized point thereon.

In testimony whereof, I have signed my name to this specification this 4th day of September, 1926.

I RALPH K. POTTER.

raic sum of the voltage of battery 8,. 

